Scientists at the University of Texas Medical School at Houston say they've started a Phase II trial of a new stem cell-based therapy for injured heart muscle.

During Phase I of the trial, researchers said patients were treated safely with intravenous adult human mesenchymal stem cells (Prochymal) after a heart attack. They experienced fewer arrhythmias, improved heart and lung function and improvement in overall condition.

"We are able to use a stem cell product that is on the shelf without prior preparation of anything from the patient, and this product appears to be able to help the heart muscle recover after a heart attack," said Dr. Ali Denktas, the trial's Houston site principal investigator and assistant professor of cardiology. "This means patients have the potential to recover quicker with less risk of an immediate secondary attack."

In many cell-based therapies, doctors harvest the patient's own cells, process them and then return them to the patient. Prochymal, developed by Osiris Therapeutics Inc., contains adult mesenchymal stem cells from healthy donors, the scientists said.

The researchers Monday enrolled the first patient for the Phase II, double-blind study at the Houston site.

Results from Phase I of the multi-institution trial are reported in the Journal of the American College of Cardiology.